Hi Vic,
Sounds like you are talking about a mobile-specific version of your website and not a responsive website.
I've saw this problem recently and it was because the mobile version of the site was not canonicalized properly to the desktop site.
In this case, the mobile page titles were left blank and Google generated their own by using H1 headings and the URL for branding. When the mobile site was canonicalized correctly, Google quickly started using the same specified titles as the desktop site.
To get this working properly, your desktop website should have something that looks like this:
href="http://m.example.com/page-1">
And your mobile site should have something like this:
This example was taken from Google's Mobile SEO configurations guide.
Check if you have this in place. If not, add it!
The only other time I've seen an issue like this was when the brand name wasn't actually in the page title. Google took what was specified as the WordPress 'Site name' and added that the end of all titles that had no branding.
By what you said, it sounded like you DO have branding in your titles, but if you don't, definitely add it the way want it to appear and don't make Google guess.
Cheers,
David